1. Field of the Invention
The present invention relates generally to a device and method for a dental articulator for use with dental model casts, and, more specifically, to a dental articulator that is easily adjustable by the dental laboratory technician and/or dentist to align, as desired, the upper and lower dental model casts.
2. Background Art
Dental articulators, which hold and align together positive dental impressions, are well known in the prior art. Articulators are used to align the upper (maxilla) dental model with the lower (mandible) dental model, to simulate current or desired occlusion. By recreating the teeth and their occlusion (alignment) in model form, false teeth, caps and other dental prosthetics can be made in the precise size and shape necessary for the patient's mouth.
To create the dental models (casts), the dentist makes a negative impression of the patient's teeth. This impression may be a full mold (bilateral) or a partial quadrant mold (unilateral). The impression is obtained by filling a tray with thermoplastic material, and holding it against the patient's teeth and gums. After the thermoplastic material partially hardens (sets up), the tray is removed, leaving the negative impression of the teeth.
To form a positive impression of the teeth and their position, pourable hardenable stone, often called yellow stone, is poured into the negative impression. The positive impression is allowed to harden, and is then removed from the negative impression, forming a precise positive model of the teeth and their placement. The hard positive impression is then pressed into a forming mold containing new yellow stone. Forming molds, also known as “molds”, “model formers”, or “cast formers” are typically made of rubber or silicone, and are used to make the dental models. The yellow stone in the forming mold is in a flowable state and forms the base of the dental cast. The positive impression bonds with the new yellow stone base, excess yellow stone is scraped away, remaining yellow stone is allowed to harden, and the complete cast or dental model is now formed. This cast or dental model is then removed from the forming mold. The casts or models (upper and lower) are then attached to a dental articulator, which emulates the patient's jaw for aligning the upper and lower teeth/casts.
The prior art describes various devices and methods for fashioning and securing the dental cast base to the positive impression. Prior art also describes various devices and methods for securing the dental casts to a dental articulator.
Representative of the early prior art for dental cast bases are devices described in Tuccillo et al, U.S. Pat. No. 3,510,947, and Beckwith, U.S. Pat. No. 4,319,875. These patents utilize bases having female plastic snap receivers. The positive impressions are fabricated with male studs, which snap into the female snap receivers of the base. This requires precise alignment of each male stud to properly mate with the female receiver. Repeated use wears down the male stud, causing loose snapping with the female receiver, thus making the alignment loose.
An alternative base system is described in Cho, U.S. Pat. No. 5,622,497, wherein a plastic base is adhered to a positive impression with a layer of stone material. The plastic base has a slot in which a disk is inserted and secured with a setscrew. The disk is attached to a stem having a ball at the other end, which connects to a reusable articulator. This system requires plastic bases that are relatively expensive, as is the non-disposable dental articulator.
The most common type of base system, however, is the type utilized in a series of patents issued to Huffman (U.S. Pat. Nos. 4,533,323; 5,548,581; 4,734,033; and 4,842,242). These patents and several others utilize base forming molds. Soft stone material is placed into a (typically) rubber base forming mold having a continuous sidewall, a floor and an open top. A hard positive impression is pressed into the soft stone material, excess overflow material is scraped away, and the soft stone material allowed to harden, adhering to the positive impression. The base and positive impression combine to form the dental cast, which has a uniform appearance due to the similar stone used in both the base and positive impression.
A variety of prior art methods for affixing dental casts made by pressing positive impressions into base forming molds to dental articulators are known. Young, U.S. Pat. No. 5,605,456, utilizes a cam clamp of the type used to secure automotive hoses. This hose clamp is wrapped around the base of the dental cast, and secured to a substantial dental articulator. Callne, U.S. Pat. No. 5,221,203, utilizes a wire loop that clips into brackets integral with the top of the base. The wire loop is attached to a screw wheel adjustable dental articulator. Both systems require articulators that are difficult to use and are expensive.
The Huffman patents utilize a variety of means to secure the dental base/cast to an articulator. Huffman utilizes a disposable single-use plastic articulator having hinged articulator arms with socket balls that snap into retention sockets mounted to the dental cast base. The retention sockets may be inserted into the still soft stone (Huffman '323), which requires the “proficiency and expertise of the technician” to decide when to insert the mounting such that proper alignment and securement is achieved. Other Huffman methods involve slots formed in the base by a shelf protruding into the interior cavity of the base forming mold. When the forming mold is removed (peeled off), slots and/or channels remain, into which a ridge tab is inserted and glued. The ridge tab has a socket that accepts a socket ball of the single-use articulator. When the upper and lower casts are aligned, a drop of quick drying glue is placed on the socket ball, and held until set. Some of the limitations of the Huffman devices are: 1) the difficulty in positioning the upper and lower casts while gluing their socket joints; 2) inability to make adjustments after gluing the socket joints; 3) inability to make adjustments/corrections to the lateral and vertical placement of the ridge tabs after gluing; 4) difficulty in storing dental casts due to space taken by the non-removable articulator; and 5) expense associated with not being able to reuse articulators on different casts.
Braun et al, U.S. Pat. No. 4,522,591 discloses an articulator for holding dental models. An upper mounting having a housing holds the upper jaw model and a lower mounting holds the lower jaw model and a cover is fastened to the housing of the upper mounting. The internal chamber of the housing holds a movable disk-shaped component which has a hinged socket extension that protrudes through a lower opening in the bottom of the housing and holds a ball to form a ball-and-socket joint. The ball has a threaded extension arm bolt that extends through an opening in the extension and has a mounting shoe fastened at the end thereof, which serves as the connection to the jaw model, which fits into the shoe. A shim is disposed in the internal chamber above the ball and has a concave contacting surface conforming to the surface of the ball. A threaded bolt extends through the cover above the shim and has a disk handle at its upper end. When the threaded bolt is turned, the front surface of the bolt pushes against the shim and presses it against the ball, causing the ball to be pressed against the internal wall of the extension and lock it into the desired position.
Cohn, U.S. Pat. No. 4,797,097 discloses a dental articulator for hingably retaining a pair of dental castings which comprises a pair of attachment members, each adapted to engage one of the castings and a hinge unit including two pivotally interconnected retaining members, each adapted to pivotally engage one of the attachment members by means of at least one ball and socket which may be selectively and reversably immobilized. The hinge unit further includes a hinge connection which provides a pair of pivot axes disposed in spaced apart parallel relationship, so that each retaining member is oriented to pivot about one of the axes; the hinge unit further provides for the reversible separation of the retaining members. In some embodiments, the ball portion of the joint is located on the retaining member and the socket on the attachment member, and in others, the ball is on the attachment member and the socket on the retaining member. The ball joint may be selectively or reversably immobilized by means of a locking screw threadedly mounted in the socket which engages the ball.
Farrell, U.S. Pat. No. 5,007,829 discloses a dental articulator having a posterior articulating assembly, an anterior incisal support assembly and a mold assembly. The posterior articulating assembly includes a ball and socket joint and a pivot joint. The ball and socket joint has a socket member which is operably coupled to the pivot joint and a ball member which is operably coupled to a first teeth cast. A set screw is threadedly mounted in the socket member to frictionally engage and lock the ball member at a desired position. The pivot joint has a pivot member operably coupled to a support member for joining the pivotal joint to a second teeth cast. The anterior incisal support assembly has an incisal pin operably joined to the first teeth cast and an incisal plate, which cooperates with the incisal pin, joined to the second teeth cast. The mold assembly has a plurality of molds each having an aperture in each of an anterior and posterior portion of the mold and an associated alignment protrusion, in close proximity to the aperture, for aligning joining members, to be cast into the first and second teeth casts, for connecting the first and second teeth casts to the ball member and the support member.
Pacino, Jr. et al, U.S. Pat. No. 6,508,646 discloses a securable mounting for an articulator for dental casts for receiving a ball portion of the articulator. The mounting comprises a rear wall, a bottom wall and laterally spaced side walls with extensions that form a partial cup or socket. A rectangular tongue connected to the rear wall is adapted to be inserted into a groove of the dental cast, and the ball portion of an articulator arm assembly is received in the partial cup or socket and secured by a screw engaged in the bottom wall of the mounting.
My previous U.S. Pat. No. 6,382,969, discloses a dental articulator system including a device and method of forming dental casts having a posterior clip. The posterior clip has a line of holes that receive male bulbous protrusions on the backside of a clip plate. A shaft extends outwardly from the front side of the clip plate and has a ball at its outer end which is received in a socket of at least one articulator arm to form an adjustable ball and socket joint. The adjustable ball and socket joint is secured in place with a hand tightenable screw threadedly engaged in the socket which applies force to the ball impinging it against the inner wall of the socket. The ball has dimples on its exterior surface that engage resistance nibs on the interior surface of the socket to lock the ball in place.
My published patent application 2008/0050694 discloses an improvement to the dental articulator of my U.S. Pat. No. 6,382,969, wherein reusable articulator arms are attached by adjustable ball and socket joints to the dental cast base during the base formation process. The adjustable ball and socket joints are secured in place with a hand tightenable screw which applies force through a plunger to the ball, impinging the ball against the inner wall of the socket of the ball and socket joint. Gross and fine horizontal alignment and vertical alignment are accomplished by adjusting the orientation of the articulator arm ball and socket joint. It does not require the use of glue, and the articulator arms can be re-used and interchanged between different sets of casts.
Callne, U.S. Pat. No. 7,112,061 discloses a dental articulator for connecting first and second dental models which includes upper and lower arms hingedly connected at their rear ends by a hinge. Each arm front end is connected by a coupling to a dental model. Each coupling includes a ball connected at lateral sides to the arm front end which has truncated front and rear sides, a central bore therethrough, and a concave rear socket having a central bore therethrough, a model connector having a neck with a concave end and an anchor at the opposed end extending from opposed sides of the neck. A threaded fastener extends through the central bore joining the model connector and rear socket to the ball such that the rear socket and model connector are movable rotationally, up and down, and side to side on the ball to a selected position. Each model connector is inserted into a rear bore of a mold such that the neck is disposed in the bore and the anchor is in the interior space of the mold and becomes cast into the model after a plaster, typically a pourable hardenable stone is poured into the interior space of the mold and hardens. Upper and lower dental models each include a holder of an incisor spacing assembly co-cast into the base which hold an incisor pin for adjusting the vertical spacing between the fronts of the dental models.
Some of the problems with the ball mounting arrangement of the Callne Patent, U.S. Pat. No. 7,112,061, are that it requires several small parts that can become lost or misplaced, it is difficult to assemble the rear socket and the model connector onto the ball, and the amount of rotational movement is limited by the difference in diameters between the outside diameter of the bolt and the inside diameter of the bore through the ball.
One of the problems associated with dental articulators having articulator arms that are attached to the dental cast by adjustable ball and socket joints in which the ball is secured in place with a set screw threadedly mounted onto the socket is that the set screws are very small and are prone to being accidentally dropped and easily lost. Another problem with small set screw members is that their tip end has a very small surface area relative to the surface of the ball, thus, it is difficult to apply sufficient force to effectively frictionally engage the ball against the inner wall of the socket to prevent slippage, and they are prone to cause galling of the ball surface.
One of the problems associated with dental articulators which provide a shim or plunger between the set screw and the ball is that the shim or plunger is small and difficult to install and remove and can be accidentally dropped and easily lost. Another problem with the dental articulators which provide a shim or plunger between the set screw and the ball is that the shim or plunger is typically unsupported and can drop into the socket cavity making it difficult to install and properly position the ball in the socket.